This invention relates to a method of producing a temperature sensor provided with lead lines or planar lead terminals and, more particularly, a temperature sensor comprising a thermistor. The invention also relates to a method of mounting such a sensor to a circuit board.
A thermistor element with a negative temperature coefficient (or an NTC thermistor element) is usually used as the temperature sensing element for such a temperature sensor and is sometimes directly contacted to a target object, such as a CPU carried on a mother board, in order to accurately measure its temperature. FIGS. 10A and 10B show an example of prior art temperature sensor 101 of this type for detecting the heat generated by a CPU 2. The prior art temperature sensor 101 is characterized as having lead lines 106 and 107 which are made, for example, of a plated wire such as a hard copper or steel wire covered with copper or stranded soft copper wires and hence have no elasticity. Thus, it was necessary to use an adhesive agent 109 to securely attach the temperature sensing element 108 of the sensor 101 to the DC fan 3 as shown in FIG. 10A or to adjust the length of the lead lines 106 and 107 according to the distance between the circuit board 5 and the DC fan 3.
By the method of using the adhesive agent 109 to attach the temperature sensing element 108 to the DC fan 3 as shown in FIG. 10A, an extra step for the attachment becomes necessary in the production process and the positioning is not an easy task. By the method of adjusting the length of the lead lines 106 and 107 to make the contact between the temperature sensing element 108 and the DC fan 3 as shown in FIG. 10B, the lengths of the two lead lines 106 and 107 must be individually adjusted. Vibrations of the DC fan 3, furthermore, make it difficult to maintain a constant positional relationship between the temperature sensing element 108 and the DC fan 3, causing difficulties in making an accurate temperature detection.
For producing temperature sensors provided with planar lead terminals, the lead terminals are produced from a lead frame in order to automate the assembly process and to reduce variations in the accuracy in shapes and sizes. FIG. 11 shows a lead frame 151 to which is attached a temperature sensing element 152. The lead frame 151 is molded so as to comprise a linearly elongated belt-shaped base part 151a and a plurality of pairs of planar lead parts 151b extending perpendicularly from the base part 151a. The temperature sensing element 152 is of a structure having terminal electrodes 152a on its two mutually oppositely facing terminal end surfaces and is inserted in the gap between the tip sections 151c of the pair of planar lead parts 151b. The tip sections 151c of the planar lead parts 151b and the terminal electrodes 152a of the temperature sensing element 152 are electrically connected by using a solder material (not shown) or the like.
It is not easy, however, to thus insert temperature sensing elements 152 into the gaps formed on the lead frame 151 in a neatly aligned manner in the direction of the thickness because the contact surface areas between the tip sections 151c of the planar lead parts 151b and the temperature sensing element 152 are small. Even after temperature sensing elements are inserted, another problem is that they cannot always be positioned stably with respect to the tip sections 151c of the planar lead parts 151b in terms of the orientation (as shown in FIG. 12A) or the position (as shown in FIG. 12B).